| AVS 56th International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF-WeM |
| Session: | Nanostructuring Thin Films I |
| Presenter: | F.S. Teixeira, University of Sao Paulo, Brazil |
| Authors: | F.S. Teixeira, University of Sao Paulo, Brazil M.C. Salvadori, University of Sao Paulo, Brazil M. Cattani, University of Sao Paulo, Brazil I.G. Brown, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
We describe our electrical, optical and structural studies of sub-nanometer composite films formed using a pulsed cathodic arc plasma gun to implant 49 eV gold ions into PMMA (polymethylmethacrylate) thin films (~ 50 nm thick). Electrical resistance measurements in situ as a function of implantation dose (up to 2 x 1016 atoms/cm2) show a conductivity increase that is well described by the percolation theory power law σ/σ0 ≈ (x - xc)t, where σ/σ0 is the measured metal/insulator composite conductivity ratio, x is the normalized concentration of the conducting phase atoms, xc is the normalized critical concentration (percolation threshold) below which the composite has zero conductivity, and t is the critical exponent. For our Au/PMMA composite we found σ/σ0 ≈ (x - 0.4)1.65, where xc corresponds to a critical dose ϕc = 1.0 x 1016 atoms/cm2. We point out that the low energy implantation used here does not create any target vacancies or carbonization, which can occur for incident ion energy greater than about 100 eV, and thus that the electronic transport properties of the composite formed here are due only to the gold phase embedded in the original polymer. TEM (Transmission Electron Microscopy) images reveal that the gold phase is a shallow-buried sub-10 nm layer consisting of a distribution of nanoclusters (diameters ≈ 2 nm – 5 nm for implantation dose ϕ < ϕc), spontaneously aggregated from the implanted gold ions, evolving to larger clusters as the dose increases. The computer simulation software TRIDYN, a dynamic version of the widely used TRIM (Transport and Range of Ions in Matter) that is more suitable when compositional changes are induced by the implantation itself as is the case here, gave very good predictions for the intermixed layer width and ion range, both with values lower than 10 nm. UV-Vis optical spectroscopy (ultraviolet to visible wavelength range) of the samples showed localized plasmon surface resonance effects from gold nanoparticles. SAXS (Small Angle X-ray Scattering) analysis was used to study the fractal character of the growth dynamics, the correlation lengths, and the size of agglomerates and elementary clusters. We related SAXS and UV-Vis data to percolation electrical behaviour. Note that the entire material is composed of a sequence, from substrate to surface, of PMMA thin film, shallow-buried composite film of nanoclusters, and an ultra thin film of unaltered polymer. These three layers can be electron beam lithographed at the same time, a highly desirable feature for application of the material for organic electronics/photonics.